A wheel-type ultrasonic inspection device transmits ultrasonic sound waves into a work piece, e.g., a metallic piece, via an intervening liquid. The body of liquid serves as a carrier for the ultrasonic sound waves. The inspection device analyzes sound energy reflected back from the surface and from within the work piece to identify defects, e.g., cracks or pockets, therein. The inspection device includes a hollow wheel structure carrying therewithin the body of liquid and the ultrasonic transmitters/receivers. The liquid remains at the well, i.e., bottom, of the wheel as it rolls relative to the surface of the work piece. In a typical application, the inspection device as a whole remains stationary while the work piece moves therepast contacting the exterior of the wheel structure. The wheel structure thereby rotates by virtue of the work piece moving therepast. The ultrasonic transmitters/receivers, by appropriate mechanical mounting, remain directed downward toward the body of liquid and toward the surface of the work piece. In this manner, the device maintains the intervening liquid in place between the ultrasonic transmitters/receivers and the surface of the work piece under inspection. Reflected ultrasonic sound waves represent surface and internal conditions along the length of the work piece under inspection.
U.S. Pat. No. 4,615,218 entitled ULTRASONIC WHEEL PROBE WITH ACOUSTIC BARRIER issued Oct. 7, 1986 to D. Pagano discusses some history of wheel-type inspection devices and discloses a device having a vertically moveable acoustic barrier interposed between the ultrasonic transmitters/receivers. The barrier extends downward and into the body of liquid and bears against the inner surface of the tire. The acoustic barrier blocks xe2x80x9ccross-talkxe2x80x9d directly between the transmitters/receivers thereby making reflected sound energy, i.e., reflected from the surface or internal portions of the work piece, predominate sound energy available for analysis. A spring urges the acoustic barrier against inner surface of the tire, i.e., the barrier moves vertically relative to the hub of the device but remains held downward against the inner surface of the tire. As the tire rolls relative to the surface of the work piece, variations in surface contour cause compression of the tire structure and cause the barrier to move relative to the hub structure of the inspection device. The barrier remains in contact with the inner surface of the tire and blocks signal xe2x80x9ccross-talkxe2x80x9d directly through the body of liquid.
Pagano detects vertical movement of the barrier relative to the hub, and thereby establishes a basis for calculating the current distance between the ultrasonic transmitters/receivers and the surface of the work piece under inspection. More particularly, Pagano uses sound energy reflected from the barrier itself to calculate its vertical displacement relative to the wheel hub structure. Reflected sound analysis incorporating a signal taken from the sound barrier, i.e., a position calculation, accounts for the variable distance between the transmitters/receivers to detect surface and internal defects in the work piece. Thus, Pagano by signal analysis executes surface tracking, i.e., calculates the distance between the ultrasonic transmitters/receivers and the surface of the work piece, to accomplish defect gate triggering of the reflected sound energy.
U.S. Pat. No. 4,763,526 entitled ULTRANSONIC WHEEL PROBE WITH IMPROVED ACOUSTIC BARRIER issued Aug. 16, 1988 also to D. Pagano shows a similar inspection device but employs a modified method of detecting vertical displacement of the barrier relative to the wheel hub structure.
In either case, Pagano maintains by spring bias the acoustic barrier against the inner surface of the tire to eliminate cross-talk and detects vertical displacement of the barrier to calculate the varying distance between the ultrasonic transmitters/receivers and thereby perform reflected sound analysis relative to the work piece under inspection.
It would be desirable, however, to simplify the method of reflected sound energy analysis by maintaining a constant pseudo-focal point within the work piece.
A wheel-type transmit/receive ultrasonic inspection device establishes a constant length internal liquid sound path by mounting the ultrasonic transducers in fixed relation to a surface tracking structure. The resulting sensor head maintains contact with the inner surface of the tire while concurrently maintaining a fixed distance between the ultrasonic transducers and the surface of the work piece under inspection. As a result, reflected sound energy analysis becomes simplified by virtue of a constant-depth pseudo-focal point.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation of the invention, together with further advantages and objects thereof, may best be understood by reference to the following description taken with the accompanying drawings wherein like reference characters refer to like elements.